Pregnant women with normal body mass index could safely put on 25 to 35 pounds of extra weight during pregnancy.
At the early stage of pregnancy, vomiting and nausea might cause a small amount of weight loss.
Usually the symptoms of morning sickness subside naturally within the 16th week of pregnancy.
Health experts fear that weight loss during pregnancy could be a sign of excess fat metabolism, which might elevate the ketone level in the maternal blood. However, researchers at the University of Linkoping, in Sweden, reported in the journal Obstetrics & Gynecology that obese women could safely lose a few pounds during pregnancy. The findings showed that obese pregnant women in the second and the third groups who gained fewer pounds during pregnancy, less than the amount recommended by the Institute of Medicine, or even lost some weight, had a lower risk of undergoing cesarean section than obese women who did put on the extra weight as recommended by IOM. The study revealed that 24 per cent of pregnant women with body mass index between 35 and 40 who gained the IOM recommended weight needed a cesarean section, whereas only 17 per cent of women with similar body mass index who lost weight during pregnancy had a C-section. Moreover, babies born to obese women who gained fewer pounds or even lost some weight during pregnancy are as healthy as babies delivered by women who gained the IOM recommended weight.
Although losing some weight during pregnancy might bring down the risk of C-section or giving birth to large newborns, it could slightly increase the risk of giving birth to small-for-gestational-age newborns. In an earlier study, researchers at the Saint Louis University School of Medicine found that losing weight during pregnancy is beneficial for pregnant women suffering from gestational diabetes.

If you are obese or a morbidly obese pregnant woman, you can maintain your body weight or lose some excess flab by combining proper diet with exercise. According to the Institute of Medicine (IOM) weight guidelines, during pregnancy, underweight women with body mass index below 18.6 should gain between 28 and 40 pounds of weight.
Overweight women with body mass index between 25 and 30 could gain 15 to 25 pounds of weight, and obese woman could gain 11 to 20 pounds of weight. A small amount of weight loss, especially if you are obese or overweight, will not harm the growing fetus. After a period of rapid weight gain, the weight gain curve might reach a plateau or it might even dip slightly. Gaining fewer pounds or even shedding a little body weight during pregnancy is beneficial for both the expectant obese mother and her baby. Obese women are more likely to give birth to babies with neural tube defects and congenital heart problems. Nausea or morning sickness that occurs in the first trimester of pregnancy is primarily triggered by the hormonal changes that occur during this phase of pregnancy.
Moreover, during the early phase of pregnancy, many women develop a strong aversion towards certain food items.
The extra calories stored in your body could supply your baby the fuel needed to sustain growth and development.

As long as you are consuming the essential nutrients in the right proportion, you need not be bothered by minor fluctuations in weight. It is advisable to check the ketone level if a pregnant woman experiences excess nausea and vomiting. If nutrient deficiency occurs throughout pregnancy, the baby will be born with a small head and underdeveloped brain. In addition, most obese women do not lose all the weight they had gained during pregnancy, which further aggravates their obesity related complications. Researchers found that obese pregnant women with gestational diabetes who maintained their weight or experienced weight loss gave birth to normal sized babies. Moderate activities such as walking at a moderate speed, at least for twenty minutes, daily, could burn the excess calories. To prevent morning sickness eat a saltine cracker or a piece of bread before getting out of bed in the morning. A calorie dense diet packed with junk foods might elevate your weight but it will deprive you and your unborn child of essential nutrients.